1. Field of the Invention
The present invention relates to a light-emitting module and an image projection apparatus using such a light-emitting module, for example, relates to a reflection type light-emitting module having a light emitting diode (LED) chip as a light emitter and an image projection apparatus using such a light-emitting module.
2. Description of Related Art
Patent document 1 suggests a reflection type light-emitting module composed of a combination of a reflector having a concave reflection surface and a light emitting diode (LED) chip. The light-emitting module is structured as a so-called reflection type LED which emits only light reflected by the reflector. With this structure, an electrode lead connected to the LED chip also functions as a heat sink, thus permitting a certain degree of improvement in the efficiency to. Patent document 2 suggests a reflection type light-emitting module composed of a plurality of LED chips arranged in one reflector having a concave reflection surface. This light-emitting module is configured such that distribution of light of the plurality of LED chips is performed on one reflection surface, thus permitting higher intensity to be achieved.
Patent document 3 suggests a mobile device composed of a combination of a transmission type liquid crystal element and three LEDs arranged on the back side thereof. The three LEDs correspond to three primary colors RGB, respectively, and are configured to illuminate images of the respective colors displayed by the transmission type liquid crystal element by being driven in a time shared manner. Patent document 4 suggests a light source device which, by using three LEDs corresponding to three primary colors RGB, synthesizes light of the respective colors with a dichroic prism.
If the light-emitting module described in patent document 1 is assumed to be used as, for example, an illumination light source device for a projector, a plurality of light-emitting modules need of the same type need to be arranged in parallel for the purpose of achieving higher intensity. The parallel arrangement of a plurality of light-emitting modules results in overall upsizing and also inefficient illumination for a display panel. In the light-emitting module described in patent document 2, a plurality of LED chips are used for one reflection surface, thus resulting in a large substantial size of a light source. As a result, the angle of light distribution is very large, thus leading to failure to achieve a light-emitting module with excellent light distribution characteristics and high efficiency.
On the other hand, in the mobile device described in patent document 3, an illumination optical system is not used which condenses illumination light from the LEDs and directs it to the transmission type liquid crystal element, thus resulting in failure to efficiently illuminate the transmission type liquid crystal element and thus failure to achieve a bright projection image. The light source device described in patent document 4 has a dichroic prism for the purpose of achieving full color, which is disadvantageous in terms of cost and size. That is, due to the configuration such that color synthesis is performed by the dichroic prism, not only the dichroic prism leads to cost increase, but also space for arranging the dichroic prism needs to be ensured. Therefore, the light source device is not suitable for an image projection apparatus which needs to be small in size and low in cost.                [Patent Document 1] JP-A-2005-322701        [Patent Document 2] JP-A-2002-9347        [Patent Document 3] JP-A-H11-295690        [Patent Document 4] JP-A-2005-189824        